Crude Protein Calculator
Calculate protein content using the Kjeldahl method and nitrogen conversion factors
Calculate Crude Protein Content
Kjeldahl Method Parameters
Titrant volume for blank test
Titrant volume for sample
Molarity of titrant (usually H₂SO₄)
Usually 1 for HCl (default)
Mass of sample analyzed
6.25 for general foods (16% N in protein)
Usually 1 (no dilution)
Protein Analysis Results
Formula: CP(%) = N(%) × Jones' factor × F2
Calculation: 0.000% × 6.25 × 1 = 0.00%
Classification: Very low or no measurable protein content
Typical Applications:
- •Non-protein materials
- •Pure carbohydrates
- •Fats and oils
Example: Meat Sample Analysis
Kjeldahl Analysis Parameters
Blank volume (Vb): 25.0 mL
Sample volume (V1): 12.5 mL
Titrant concentration: 0.1 mol/L
Sample weight: 1.000 g
Conversion factor: 6.25 (general food)
Calculation Steps
1. Nitrogen content: N(%) = (25.0 - 12.5) × 0.1 × 1 × 1.4007 / 1.000 = 1.751%
2. Crude protein: CP(%) = 1.751% × 6.25 × 1 = 10.94%
Result: 10.94% crude protein (moderate protein food)
Common Conversion Factors
General Food
Factor: 6.25
Standard factor for most foods
N content: 16%
Seafood
Factor: 5.6
Fish, shrimp, and marine proteins
N content: 18%
Cereals
Factor: 5.4
Grains, wheat, rice, etc.
N content: 18.5%
Red Seaweed
Factor: 4.59
Marine algae products
N content: 22%
Milk Proteins
Factor: 6.38
Dairy products
N content: 15.7%
Soy Products
Factor: 5.71
Soybeans and soy-based foods
N content: 17.5%
Kjeldahl Method
Step 1: Digestion
Heat sample with H₂SO₄
Protein → (NH₄)₂SO₄
Step 2: Neutralization
Add NaOH to release NH₃
(NH₄)₂SO₄ + NaOH → NH₃
Step 3: Titration
Titrate with acid
NH₃ + HCl → NH₄Cl
Step 4: Calculation
Calculate N% and protein%
Formulas
Vb, V1: Blank, sample volumes (mL)
c: Titrant concentration (mol/L)
F1: Acid factor, F2: Dilution factor
m: Sample mass (g)
Protein Levels
Understanding Crude Protein Analysis
What is Crude Protein?
Crude protein is an estimate of protein content based on nitrogen analysis. Since proteins typically contain about 16% nitrogen, measuring nitrogen and applying a conversion factor provides a protein estimate.
Key Applications
- •Food nutrition labeling and quality control
- •Animal feed formulation and analysis
- •Agricultural research and crop evaluation
- •Industrial protein product development
Crude vs True Protein
Crude protein includes all nitrogen-containing compounds, not just proteins. True protein analysis measures only actual protein content, but crude protein is simpler and widely used for routine analysis.
The Kjeldahl Method
N(%) = (Vb - V1) × c × F1 × 1.4007 / m
Nitrogen content calculation
Method Steps
- 1. Digestion: Heat sample with concentrated sulfuric acid
- 2. Neutralization: Add sodium hydroxide to release ammonia
- 3. Distillation: Collect ammonia in boric acid solution
- 4. Titration: Titrate with standardized acid
- 5. Calculation: Calculate nitrogen and protein percentages
Note: The Kjeldahl method is the official AOAC method for protein analysis and is widely accepted for regulatory and commercial purposes.
Conversion Factors and Sample Types
General Foods (6.25)
Standard factor assuming 16% nitrogen in proteins. Used for most foods when specific factors are unknown.
Seafood (5.6)
Marine proteins have higher nitrogen content (~18%). Used for fish, shrimp, and other seafood products.
Cereals (5.4)
Grain proteins have unique amino acid composition. Used for wheat, rice, corn, and other cereal products.